i have a stock s13 redhead and i was wondering wats the highest rating gas can i use not to mess up my motor?

The lowest would be 91.

ive ran 101

ppl run 102.6 (our "racing" fuel) here no problems

Im pretty sure theres no such things as too high an octane. Too low yes, but not too high.

I've ran 116, the car will run fine, just feels sluggish if you don't advance the timing to make use of it.

Your car will make less power on higher octane unless you retune it for the higher octane.

Doesn't race gas eat up the o2 sensor?

yup..

I used 110 leaded octane on my then-stock SR20DET. Other than the O2 sensor going bad, everything else was good. That high of octane is unnecessary unless you've got a built motor that requires octane that high. For the most part, pump gas 91-octane and up will suffice.